At present, widely used as a portable information apparatus is a portable telephone. As electronic parts have been developed to be smaller in size, lighter in weight and more sensitive, various portable telephones having a portable telephone main body that is smaller in outer shape, and light in weight.
A portable telephones, in general, is provided with a main body, an antenna, which is installed on an upper part of the main body, a display screen, which displays various information such as a receiving condition of the antenna (radio wave receiving condition), information how long a battery lasts (battery lasting information) and the like, operation buttons including a plurality of number keys and function keys, a speaker and a microphone.
Recently, a portable telephone of a folder type has become more popular. The portable telephone of the folder type is generally provided with an upper main body, a lower main body, and a hinge. The upper main body is provided with the display screen for displaying the information, the speaker, and the antenna, while the lower main body is provided with the operation buttons and the microphone. The hinge connects the upper and the lower main bodies so that the upper and the lower main bodies can be folded and unfolded in such a manner that the upper and the lower main bodies make a predetermined angle that is suitable for having a talk by using the portable telephone of the folder type when the portable telephone of the folder type is unfolded.
When the portable telephone of the folder type is in a call wait state where the portable telephone of the folder type remains being folded (in a folded state), that is, the upper main body is folded with respect to the lower main body, the operations bottoms of the lower main body are covered with the upper main body. It is advantage that this prevents error operation of the operation bottoms. Moreover, when the portable telephone of the folder type is in a talking state where the portable telephone is unfolded, that is, the upper main body is unfolded with respect to the lower main body, the lower main body can be used as a voice collecting board for collecting voice. This gives such merit that the voice collecting ability of the microphone is improved.
Recently, it has become possible for the portable information apparatus such as the portable telephone to transmit a large data at a high speed. This encourages development of a display screen of the portable information apparatus having a high image quality, in response to a recent trend that the portable telephone has a color display and a dynamic image display, for example.
Used as the display screen for the portable information apparatus is a liquid crystal display apparatus that has excellent characteristics such as a thin shape, a light weight, and low electricity consumption, in general. There are a passive matrix method and an active matrix method for a display mode and a driving method of the liquid crystal display apparatus. However, a liquid crystal display apparatus of the passive matrix method, such a Super Twisted Nematic method (hereinafter, just referred to as STN) has come in practical use, because the liquid crystal display apparatus of the passive matrix method consumes less electricity and costs less.
Moreover, it has also been intensively studied for developing a liquid crystal display apparatus of the active matrix method as the display screen for the portable telephone. The liquid crystal display apparatus of the active matrix method is provided with a switching element in each pixel in order to improve display properties. Examples of the switching element (active element) are a non-linear element having two terminals, and a non-linear terminal having three terminals, while a typical switching element that has been developed so far is a Thin Film Transistor (hereinafter, denoted as TFT) that is a type of the non-linear element having three terminal.
A liquid crystal display apparatus of the active matrix method, in which the TFT is provided, has such excellent display properties that the display has an excellent brightness, a high contrast and a high response speed, for example. Because the display properties enable the liquid crystal display apparatus of the active matrix method to perform the color display and the dynamic image display in the high image quality, the liquid crystal display apparatus of the active matrix method having the TFT is regarded as the most suitable device as the display screen for the portable telephone.
In a conventional portable telephone of the folder type, it is necessary to unfold the upper main body with respect to the lower main body so as to check the various information displayed on the display screen during the call wait state. Therefore, it is so inconvenient for a user that he has to fold and unfold the upper main body with respect to the lower main body each time he checks the various information. Among the various information, the receiving condition of the antenna and the information how long the battery lasts (battery lasting information) are checked so often. Thus, it is so troublesome to fold and unfold the upper main body with respect to the lower main body every time for checking those kinds of the information.
Therefore, the Japanese Un-examined Patent Publication Tokukai No. 2000-184023 (published on Jun. 30, 2000) discloses a portable telephone that has a structure that shows, through a transparent window of a holder, the information on the display screen. However, the portable telephone recited in the publication (the portable telephone of the prior art) need display the whole region of the screen all the time even when the portable telephone is in the call wait state. Thus, the portable telephone of the prior art will have a difficulty to achieve low electricity consumption when the portable telephone of the prior art is required to have the high image quality in response to the trend that the display screen displays the color display and the dynamic image display. Moreover, it is difficult for the portable telephone of the prior art to display many pieces of the information at once because a touch screen for data input, which is provided on a display section, reduces a region where the information is displayed when the data is inputted.
At present when there is a demand for the display screen having the high image quality for the color display and the dynamic image display. Thus, the liquid crystal display apparatus of the STN method (STN liquid crystal display apparatus) has such advantages that the STN liquid crystal display apparatus consumes such a little electricity (10 to 15 mW) when the screen is as small as 2-inch size, while the STN liquid crystal display apparatus has problems of a poor brightness, a low contrast, and slow response speed, which make it difficult for the STN liquid crystal display apparatus to attain satisfactory image quality. Therefore, in order to attain the satisfactory image quality, it is necessary to use the liquid crystal display apparatus of the active matrix method that uses a three-terminal element having an excellent display ability, such as the TFT.
However, the liquid crystal display apparatus of the active matrix method has such a complicated peripheral driving circuit, compared with the STN liquid crystal display apparatus. For this reason, the liquid crystal display apparatus of the active matrix method consumes a large electricity (100 to 150 mW), even if the screen is as small as the 2-inch size, thus it is not so suitable for use in the portable telephone. Therefore, if the liquid crystal display apparatus of the active matrix method is used in an apparatus, which need display the whole region of a display screen all the time, such as the portable telephone recited in the publication, it is hard to achieve low electricity consumption in the apparatus.